1. Field of the Invention
The present invention relates to methods for fabricating an image sensor device, and in particular relates to methods for fabricating an image sensor device having microlenses with different heights.
2. Description of the Related Art
As optoelectronic devices, such as digital cameras, digital video recorders, image capture capable mobile phones and monitors, become more and more popular, the demand for image sensor devices accordingly increase. An image sensor device is used for recording a change of a photo signal from an image and converting the photo signal into an electronic signal. After recording and processing the electronic signal, a digital image is generated. In general, image sensor devices can be categorized into two main types, one is charge coupled devices (CCD) and the other complementary metal oxide semiconductor (CMOS) devices.
An image sensor device typically comprises a pixel array. Each pixel includes a photosensor that produces a signal corresponding to the intensity of light impinging on the photosensor. When an image is focused on the array, signals can be employed to display a corresponding image. In conventional technology, a microlens array is correspondingly disposed above the pixel array and used for focusing light onto the pixel array. However, despite the use of the microlens array, a large amount of incident light is not directed efficiently onto the photosensors due to the geometry of the microlens array. The focal depth of the incident light to each photosensor is varied with the incident angle of the light (i.e. chief ray angle (CRA)). Accordingly, the microlens array with different focal depths reduces photosensitivity of the image sensor device.
Layered microlens structures for a microlens array have been proposed to address such a problem. However, the poor ability to control the microlens profile, wherein substantially the same microlens shape still reduces photosensitivity of the image sensor device. Therefore, there is a need to develop a method for fabricating an image sensor device, which is capable of easily controlling each individual microlens to have a desirable height, so that photosensitivity of the image sensor device is improved.